Quantifying the coexistence of massive black holes and dense nuclear star clusters

In large spheroidal stellar systems, such as elliptical galaxies, one invariably finds a 106â-109 M⊙ supermassive black hole at their centre. In contrast, within dwarf elliptical galaxies one predominantly observes a 105â-107 M⊙ nuclear star cluster. To date, few galaxies have been found with both types of nuclei coexisting and even less have had the masses determined for both central components. Here, we identify one dozen galaxies housing nuclear star clusters and supermassive black holes whose masses have been measured. This doubles the known number of such hermaphrodite nuclei â- which are expected to be fruitful sources of gravitational radiation. Over the host spheroid (stellar) mass range 108â-1011…